This invention relates generally to apparatus for making a non-contact angular deflection measurement and more particularly, but not by way of limitation, to apparatus for magnetically detecting across a magnetically permeable wall the rotational movement of a member about an axis.
A consistometer or a viscometer is a known type of device in which the angular displacement, or rotation, of an internal shaft within a pressurizable vessel is used to determine properties of a fluid contained in the vessel. To measure such angular displacement, various types of sensing apparatus have been used. These apparatus include spring-biased sensing elements, indicia-containing dials visible through sight glasses, and electrical signals generated by means of strain gauges or linearly variable differential transformers. Magnetic and electromagnetic devices can also be used. A particular example of a magnetic sensing device is disclosed in U.S. Pat. No. 4,466,276 to Ruyak et al. In the Ruyak et al. device torque is transferred through a magnetic coupling to a potentiometer.
In many of the aforementioned examples, the sensing devices, or at least some operational parts thereof, are placed in an environment of the consistometer or viscometer wherein adverse conditions for such parts are found. These conditions result from the high temperatures and pressures that can exist in the vessel or from properties of the fluid contained in the vessel. In such an environment, the accurate measurement of the angular deflection is made difficult because the operational parts have to be compatible with the adverse conditions in the vessel. Sensing devices which have such compatible components can be relatively expensive because of the special construction needed to withstand the adverse conditions. They can also be expensive to maintain and replace because it can be difficult to remove internal components from inside the vessel. Additionally, some of these devices can produce friction in bearing surfaces which affects the small torsional forces that cause the angular deflections of the shaft, and therefore generate inaccurate readings.
In view of the aforementioned shortcomings, there is the need for an improved apparatus having sensing or detection components that are located outside an adverse environment in which is located the element whose angular deflection or rotation is to be monitored. This would obviate the need to construct such components so that they can withstand the adverse conditions. Such components also would be more easily maintained. Such features would provide a more cost effective measurement apparatus. There is also the need for such a measurement apparatus to be constructed so that it is not adversely affected by friction in bearing surfaces. Such an improved apparatus should also be capable of directly indicating the actual angle of rotation and the actual location of the displacement of the monitored elements. There is still the further need for such an apparatus to have a construction which can be readily retrofitted to existing devices, such as viscometers and consistometers, whose angular displacements are to be monitored. This retrofitting feature would be particularly useful, for example, with a sight-glass indicator type of viscometer or consistometer whereby the need to make manual inspections and logs would be obviated.